Like any other service I would always recommend comparing three different mortgage advisors before choosing one. Even if you have a recommendation from a friend or relative, still have a consultation and compare them with two others. Also follow the tips from the money advice service for choosing an adviser here:
https://www.moneyadviceservice.org.uk/en/articles/choosing-a-mortgage-shop-around-or-get-advice
I did all the above to find esther at independent mortgage experts and she did a brilliant job when our previous lender suddenly decided they weren't interested in helping when we wanted to move. Esther turned a desperate situation into massive relief when she found us a mortgage with a high street lender way cheaper than we expected to get. Our fixed rate is due to end next year and we'll be contacting esther to get another fix deal.